Speeding fine in Switzerland via mail notification

gr.ch is the domain for the Grisons Canton. I don't see a site on busses.gr.ch though.

Did they tell you where, and how fast they caught you?

Did you rent the car? Usually the country IDs the car through the registration number, which means that your rental company would have gotten it first. They then send you a notice (usually with an administrative fee), and forward your name and contact information to the official agency. The agency then has the option of sending it out directly to you.

So I would definitely check with your rental company if you aren't sure about this.

Are you sure it’s not bussen with an n?
And were you driving in canton Graubünden? If the fine is legitimate and from the Graubünden cantonal police, you can check and pay online here
https://www.gr.ch/EN/institutions/administration/djsg/kapo/Seiten/welcome.aspx
Click “online desk” and from there, it will direct you to a page where you can search for your ticket number and pay the fee online. This page is bussen.gr.ch which is why I asked about spelling.

I first received an email notice from the rental car company (+excessive fee) stating they are forwarding my contact information to the Swiss government. About a month later, I received an letter stating the location, speed and calculated fee. The letter had the information to pay online.

Got one in Geneva in 2023. Sixt notified me first, then the canton's mail arrived shortly thereafter.

I paid the fine online via the ticket issuer's website - easy peasy.

Sixt simply passed along the fine for me to pay. If I didn't then there would be a fine+fee from them. I avoided that, thankfully.